The present invention relates to a liquid crystal panel, and particularly to an active matrix liquid crystal panel.
A typical active matrix liquid crystal panel includes transistors for driving pixel electrodes, a driving substrate having the transistors thereon, and a counter substrate having a counter electrode thereon, such that the two substrates have a liquid crystal layer interposed therebetween. FIG. 5 is a schematic plan view of a typical active matrix liquid crystal panel. Referring to FIG. 5, the liquid crystal panel 1 includes a driving substrate 11 and scanning lines 13 and signal lines 15 on the display surface of its driving substrate 11, such that the lines 13 and the lines 15 are provided perpendicular to each other. The scanning lines 13 and the signal lines 15, intersecting each other, form an array of pixels 16. Each of the pixels 16 includes a transistor 17 having a gate connected to the corresponding scanning line 13 and a source and a drain connected to the corresponding signal line 15 and a pixel electrode 19. The driving substrate 11 also has an alignment film (not shown in FIG. 5) covering the components on the substrate 11.
In the liquid crystal panel 1 provided with the driving substrate 11 described above, the scanning lines 13 and the signal lines 15 are provided adjacent to the pixel electrodes 19. This structure generates transverse electric fields between the scanning lines 13 and the pixel electrodes 19 and between the signal lines 15 and the pixel electrodes 19. These transverse electric fields consequently cause local irregular orientation of liquid crystal molecules in the liquid crystal layer over the pixel electrodes 19. It is known that light leaks in these regions where the liquid crystal molecules are oriented irregularly (referred to as reverse-tilt domains). The reverse-tilt domains parallel to the signal lines 15 and the scanning lines 13 are indicated by d1 and d2, respectively, in FIG. 5.
Referring now to FIG. 6, Japanese laid-open Patent Application Publication No. 2002-40455 discloses a liquid crystal panel 2, in which the aforementioned alignment film is rubbed in a rubbing direction x substantially parallel to the signal lines 15, thus preventing irregular orientation of liquid crystal molecules in the liquid crystal layer caused by transverse electric fields between the signal lines 15 and the pixel electrodes 19, and therefore preventing reverse-tilt domains d1 parallel to the signal lines 15.
However, the liquid crystal panel 2, which is capable of preventing reverse-tilt domains d1 parallel to the signal lines 15 as described above, is not effective in preventing reverse-tilt domains d2 parallel to the scanning lines 13. For this reason, the reverse-tilt domain d2 parallel to each of the scanning lines 13 is light-shielded with a mask provided around the corresponding pixel 16.
It is also known that, in a typical liquid crystal panel, an external force applied to the panel surface such as pressing the panel surface causes the liquid crystal layer underneath the panel surface to flow, and consequently, the associated reverse-tilt domains move according to the flow. In the liquid crystal panel 2 in FIG. 6, for example, pressing the panel surface causes the liquid crystal layer to flow. The reverse-tilt domain d2 generated along each of the scanning lines 13 moves toward the center of the pixel 16 in the rubbing direction x. As a result of this phenomenon, each of the reverse-tilt domains d2 moves toward the center of the pixel 16 where light-shielding is not provided. Thus, light easily leaks in such a non-shielded display area, i.e., the center of each pixel 16. Furthermore, a reverse-tilt domain which has moved to the display area remains there for several seconds even after the pressure to the panel surface has been released. As a result, this light leakage is easily noticeable, contributing to degradation of the display performance of the liquid crystal panel.
In particular, for a liquid crystal panel used in a display device with a touch panel, pressing the panel surface is unavoidable. In such a display device, light leakage caused by this press onto the panel surface is the greatest factor contributing to the degradation of the display performance.